import "Prelude"

data RealWorld = RealWorld
data IO a = IO (RealWorld -> (RealWorld, a))

@inline
unIO (IO m) = m 

instance Functor IO where
    @inline
    fmap f x = x >>= (return . f)

instance Monad IO where
    @inline
    return x = IO (\s -> (s, x))
    
    @inline
    (IO m) >>= f = IO (\s -> do
        (newS, v) = m s
        unIO (f v) newS 
    )

@inline
runIO :: IO a -> a
runIO m = snd (unIO m RealWorld)

main = runIO (return (13 :: Integer))
--
13